The nature of the changes in sexual behavior and experience which accompany aging in men and women and their relationship to alterations in circulating levels of gonodal hormones will be investigated. Different patterns of male hypogonadism in aged men will be sought in terms of gonadal-pituitary relationships and possible etiological differences. Subsequently, methods of replacement therapy will be evaluated in double-blind experiments for their effects on sexual behavior. Male paraplegics and quadriplegics will be studied in order to identify, and later correct, sexual dysfunction mediated by lowered androgen levels in blood.